In an LDI apparatus, CAD data used for designing a circuit pattern are converted into vector data format, and then contours are calculated from the vector data. After that, the contours are further converted into raster data for imaging. From the raster data, ON and OFF pixels for a laser beam are obtained. The ON pixels are irradiated with the laser beam.
FIG. 7 is a view showing a configuration of background-art LDI apparatus.
A laser source 1 is mounted on an optical table 16. The optical table 16 is disposed on a column 17 on a bed 18. A laser beam 5 emitted from the laser source 1 enters an acousto-optic modulator (hereinafter referred to as “AOM”) 4 reflected by mirrors 2 and an expander 3. A laser beam 5a modulated by the AOM 4 is deflected by a polygon mirror 6 and enters an fθ lens 7. The laser beam 5a emerged from the fθ lens 7 is deflected toward the downward direction of FIG. 7 by a reflection mirror 8, and enters a cylindrical lens 9. The laser beam 5a emerged from the cylindrical lens 9 is incident on a workpiece 10. A dry film resist (hereinafter referred to as “DFR”), a photo-resist or the like on the workpiece 10 is exposed to the laser beam 5a. On this occasion, a table 12 where the workpiece 10 is mounted moves in a sub-scanning direction (Y-axis direction in FIG. 7. The X-axis direction in FIG. 7 is a main scanning direction.) at a constant speed. A linear motor 14 moves the table 12. A pair of guides 13 guide the table 12 (Patent Document 1).
Here, the anterior focal point of the fθ lens 7 is positioned on the reflection plane of the polygon mirror 6. Of the laser beam 5 reflected by the polygon mirror 6, components parallel to the XY plane are parallel rays, and components perpendicular to the XY plane are divergent rays starting at a reflection point of the polygon mirror 6. Accordingly, the components of the laser beam 5 parallel to the XY plane are converged by the fθ lens 7 but passed through the cylindrical lens 9 as they are. On the other hand, the components of the laser beam 5 perpendicular to the XY plane are converted into parallel rays by the fθ lens 7, and converged by the cylindrical lens 9.
FIGS. 8A and 8B are views showing the position of a start sensor. FIG. 8A is a view in the X-axis direction of FIG. 7, and FIG. 8B is a view in the Y-axis direction of FIG. 7.
A mirror 11 is disposed under the left end portion of the cylindrical lens 9 in FIG. 7. A start sensor 15 is disposed in the direction of reflected laser beam from the mirror 11. In order to align the imaging start positions of rows, which mean the rows of the exposed pixels by the main scanning (X-axis direction), imaging in each scan in the main scanning direction is started when a predetermined time has passed after the start sensor 15 has detected the laser beam 5a reflected by the mirror 11 (the distance between the detection position and the imaging start position is 10 mm in the illustrated case).
The table 12 on which the workpiece 10 is mounted moves in the sub-scanning direction when the laser beam is scanning in the main scanning direction. Accordingly, when the laser beam 5 is scanned in the X direction, the scanning line by irradiation (exposure) with the laser beam 5 tilts clockwise at an angle α with respect to the X direction (main scanning direction) as shown in FIG. 9. The angle α will be referred to as “scanning angle”.
In the background art, therefore, an irradiation optics is disposed so that the scanning angle α is set to 0 with respect to the moving direction of the table 12, and an irradiation system is disposed so that the scanning line of exposure is perpendicular to the Y direction (sub-scanning direction).
Patent Document 1: JP-A-2007-94122
If the sensitivity of a photosensitive material to light (hereinafter referred to as “sensitivity” simply) is uniform, the scanning angle α can be made constant. However, some DFR (Dry Film Resist) may have a variation in its resist sensitivity. For example, assume that the output of a laser is constant, and the resist sensitivity is 50 mJ/cm2. In this case, the scanning speed of the laser beam (the number of revolutions of the polygon mirror) and the moving speed of the table must be made ⅕ of that when the resist sensitivity is 10 mJ/cm2.
However, the polygon mirror has a narrow range of stable revolution speed (which is, for example, as wide as or ½ as wide as the rated revolution speed). Accordingly, the range of possible scanning angle α is so narrow that the workpieces which can be exposed are limited in variety.